Method and apparatus for video decoding, in the presence of noise

ABSTRACT

A method and apparatus for decoding video data that is encoded by bit rate control to keep a bandwidth of a bit stream in a predetermined range are provided. The encoded video data is decoded, picture quality estimation information is estimated, the estimation including information about a bit stream size of a decoded video frame, the number of fragmented macro blocks included in the video frame, and the number of skip-mode macro blocks included in the video frame, the picture quality of the video data is determined based on a correlation between picture quality estimation information and SNR, and the video data is output by applying a picture quality improving algorithm to the video data, if the determined picture quality is lower than a predetermined level.

CLAIM OF PRIORITY

This application claims the benefit of the earlier filing date, pursuantto 35 USC 119, to that patent application filed in the Korean PatentOffice on Dec. 20, 2007 and afforded serial number 10-2007-0134331, thecontents of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a video decoding and more particularly,to a method for decoding data encoded by bit rate control.

2. Description of the Related Art

A conventional video encoder uses bit rate control to keep the bandwidthof a bit stream within a predetermined range. The bit rate controlscheme keeps the bandwidth of the bit stream constant by controlling atleast a quantization value that determines picture quality. However, thechange of the quantization value leads to fluctuation of the picturequality, which is the main cause of picture flickering and low-qualityvideo.

To reduce the bit rate control-incurred change of video quality in thevideo encoder, a video decoder should be aware of the level of picturequality. For this purpose, the Peak Signal to Noise Ratio (PSNR) of anoriginal video is calculated during encoding and is provided to thevideo decoder on a separate channel. Thus, this conventional videoencoding/decoding technology requires an additional device forperforming a PSNR calculation and an additional channel to deliverinformation about the picture quality level to provide the picturequality level information to the video decoder.

SUMMARY OF THE INVENTION

An aspect of exemplary embodiments of the present invention is toprovide a method for decoding encoded video data of a bit stream formatto high-quality video data without separately generating picture qualityinformation.

Moreover, an aspect of exemplary embodiments of the present inventionprovides a decoding method for estimating a picture quality level basedon information acquired during decoding video data and filtering thedecoded video data according to the estimated picture quality level.

In accordance with an aspect of exemplary embodiments of the presentinvention, there is provided a method for decoding video data that isencoded by bit rate control, in which the encoded video data is decoded,picture quality estimation information including information about a bitstream size of a decoded video frame, the number of fragmented macroblocks included in the video frame, and the number of skip-mode macroblocks included in the video frame is estimated, the picture quality ofthe video data is determined based on a correlation between picturequality estimation information and Signal-to-Noise Ratio (SNR), and thevideo data is output by applying a picture quality improving algorithmto the video data, if the determined picture quality is lower than apredetermined level.

The SNR can be PSNR. The SNR is estimated by the below equation and itis preferable to determine a picture quality of the video data based onthe estimated SNR.

Cost(SIZE, SKIP,4 MV)=ƒ(SIZE)·α+ƒ(SKIP)·β+ƒ(4 MV)·γ

-   -   where α, β and γ are weights and    -   ƒ(x) is a standardization function defined as

${f(x)} = \frac{X - \mu}{\mu}$

-   -   where X is a target value and u is an accumulated average.

To determine the picture quality, an SNR decrease can be calculated. Thepicture quality improving algorithm can be a PSNR improving algorithm.

In accordance with another aspect of exemplary embodiments of thepresent invention, there is provided an apparatus for decoding videodata that is encoded by bit rate control, in which a decoder decodes theencoded video data, a picture quality detector estimates picture qualityestimation information including information about a bit stream size ofa decoded video frame, the number of fragmented macro blocks included inthe video frame, and the number of skip-mode macro blocks included inthe video frame, and measures the picture quality of the video databased on a correlation between picture quality estimation informationand SNR, a picture quality improvement filter improves the picturequality of the video data received from the decoder, and a selectionswitch switches the video data selectively to one of a picture qualityimprovement filter and an external device according to the picturequality of the video data.

It is preferred that the picture quality detector measures the picturequality of the video data by calculating a decrease in an SNR estimatedusing the picture quality estimation information. The picture qualityimprovement filter can be a noise reduction filter.

BRIEF DESCRIPTION OF THE DRAWINGS

The above features and advantages of certain exemplary embodiments ofthe present invention will be more apparent from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a block diagram of a video decoder according to an exemplaryembodiment of the present invention;

FIG. 2 illustrates an exemplary video frame decoded by the video decoderaccording to the exemplary embodiment of the present invention;

FIG. 3 is a graph illustrating PSNRs improvement by use of a picturequality improvement filter in the video decoder according to theexemplary embodiment of the present invention;

FIG. 4 is a flowchart illustrating a video decoding method according toan exemplary embodiment of the present invention;

FIG. 5. illustrates a condition of an exemplary embodiment of thepresent invention;

FIG. 6 illustrates a result estimated under the condition of FIG. 5; and

FIG. 7 illustrates a coefficient between the PSNR and the greatest powersignal that is calculated by using the result of FIG. 6.

Throughout the drawings, the same drawing reference numerals will beunderstood to refer to the same elements, features and structures.

DETAILED DESCRIPTION OF THE INVENTION

The matters defined in the description such as a detailed constructionand elements are provided to assist in a comprehensive understanding ofexemplary embodiments of the invention. Accordingly, those of ordinaryskill in the art will recognize that various changes and modificationsof the embodiments described herein can be made without departing fromthe scope and spirit of the invention. Also, descriptions of well-knownfunctions and constructions are omitted for clarity and conciseness.

FIG. 1 is a block diagram of a video decoder according to an exemplaryembodiment of the present invention.

Referring to FIG. 1, the video decoder according to the exemplaryembodiment of the present invention includes a Moving Picture ExpertsGroup-4/Advanced Video Coding (MPEG-4/AVC) decoder 10, a picture qualitydetector 20, a selection switch 30, and a picture quality improvementfilter 40.

The MPEG-AVC decoder 10 receives data encoded in a bit stream format byan MPEG-4/AVC encoder (not shown) and outputs color difference signalvalues for each pixel of the received video data. Also, the MPEG-4/AVdecoder 10 provides information about the bit stream size, type and thefragmentation state of each macro block acquired during decoding theencoded data to the picture quality detector 20.

The picture quality detector 20 acquires picture quality estimationinformation based on the information received on a macro block basisfrom the MPEG-4/AVC decoder 10. The picture quality estimationinformation includes information about the bit stream byte size of acurrent received video frame, the number of skip-mode macro blocksincluded in the video frame, and the number of fragmented macro blocks.The picture quality detector 20 then estimates the Signal-to-Noise Ratio(SNR) of the received video based on the correlation between the SNR andthe picture quality estimation information. Preferably, the SNR can be aPSNR.

FIG. 2 illustrates an exemplary video frame decoded by the video decoderaccording to the exemplary embodiment of the present invention.

Referring to FIG. 2, reference character “a” denotes skip-mode macroblocks and reference character “b” denotes 4-fragment macro blocks. Thepicture quality detector 20 counts the number of the skip-mode macroblocks “a” in the video frame, SKIP and counts the number of the4-fragment macro blocks “b”, 4 MV.Preferably, the picture qualitydetector 20 calculates a reduction level in a SNR based on the videodata that standardizes the correlation between the SNR and the picturequality estimation information. A cost of the SNR of the video image ofa current frame is calculated by the below equation (1), using thecalculated reduction level.

Cost(SIZE,SKIP,4 MV)=ƒ(SIZE)·α+ƒ(SKIP)·β+ƒ(4 MV)·γ  (1)

where 60 , β and γ are weighting factors

-   -   ƒ(x) is a standardization function defined as

${f(x)} = \frac{X - \mu}{\mu}$

-   -   -   where X is a target value and μ is an accumulated average.

In one aspect, α, β and γ can be set to −0.5, 0.1, and −0.4,respectively, and X represents the bit stream byte size of the videoframe (SIZE), the number of the skip-mode macro blocks in the videoframe (SKIP), or the number of the 4-fragment macro blocks (4 MV), and μis the accumulated average of X. For instance, if 4 MV=10, 30 and 40respectively in first, second and third video frames, X=40 for 4 MV andμ is the accumulated average of the first and second video frames, i.e.20 in the third video frame.

While the picture quality detector 20 calculates a cost of an SNR of thevideo data by using the above equation (1) and determines a picturequality level of the video data based on the cost of the SNR in theexemplary embodiment of the present invention, to which the presentinvention is not limited, the picture quality level can be determined inother ways according to the correlation between SNR and picture qualityestimation information extracted during decoding.

For example, the SNRs and picture quality estimation information of aplurality of videos are measured, the consistency and regularity of theSNRs and the picture quality estimation information are analyzed, andthe correlation between SNR and picture quality information is placedaccordingly.

The selection switch 30, which includes a single input port and aplurality of output ports, selectively switches the input port to one ofthe output ports. The output ports of the selection switch 30 areconnected to an external output device (not shown) and the picturequality improvement filter 40, respectively. The selection is made amongthe output ports of the selection switch 30 based on the SNR estimatedby the picture quality detector 20. In other words, the selection switch30 compares the estimated SNR with the first predetermined threshold. Ifthe estimated SNR is less than the first threshold, the selection switch30 switches the input port to the output port connected to the picturequality improvement filter 40. If the estimated SNR is equal to orlarger than the first threshold, the selection switch 30 switches theinput port to the output port connected to the external output device.Given the first threshold of 40, if the average of SNRs received fromthe picture quality detector 20 is less than 40, the selection switch 30connects the input port connected to the MPEG-4/AV decoder 10 to theoutput port connected to an input path 31 to the picture qualityimprovement filter 40. If the average SNR is equal to or larger than 40,the selection switch 30 connects the input port connected to theMPEG-4/AV decoder 10 to the output port connected to an input path 35 tothe external output device.

The picture quality improvement filter 40 receives video data as thecolor difference signal values for each pixel from the MPEG-4/AVCdecoder 10 and cancels noise from the video data.

For instance, the picture quality improvement filter 40 filters eachpixel of the video frame and calculates the difference between thefiltered value and the original signal value. If the difference is lessthan the second predetermined threshold, the picture quality improvementfilter 40 cancels noise, determining that the pixel is noise. If thedifference is larger than the second threshold, the picture qualityimprovement filter 40 recovers the original decoded value by adding thedifference to the filtered value, considering that the pixel is notnoise but an edge. Further, the picture quality improvement filter 40compensates for a filtering-caused decrease in the value of the edge.

In accordance with the exemplary embodiment of the present invention,the picture quality improvement filter 40 filters each pixel in thevideo frame and detects and cancels noise in the video data using thedifference between the filtered value and the original signal value, towhich the present invention is not limited. Yet, the picture qualityimprovement filter 40 suffices as far as it improves the picture qualityimpaired during encoding. For example, the picture quality improvementfilter 40 is enough if it can improve PSNR as illustrated in FIG. 3. InFIG. 3, a dotted line indicates a PSNR before improvement and a soldline indicates a PSNR improved by the picture quality improvement filteras shown in an enlargement area A.

Now a description will be made of an operation of the video decoderaccording to an exemplary embodiment of the present invention.

Upon receipt of data encoded in a bit stream format by a MPEG-4/AVCencoder, the MPEG-4/AVC decoder 10 recovers color difference signalvalues of pixels included in each video frame in an MPEG-4/AVC decodingscheme. During the decoding, the MPEG-4/AVC decoder 10 providesinformation about the bit stream size, type, and fragmentation state ofeach macro block, extracted from the received data, to the picturequality detector 20.

The picture quality detector 20 acquires picture quality estimationinformation based on the information received on a macro block basis andestimates the PSNR of the video frame by equation (1).

The selection switch 30 compares the estimated PSNR received from thepicture quality detector 20 with the first predetermined threshold andselectively switches the input port connected to the MPEG-4/AVC decoder10 to an output port connected to an external output device or a picturequality improvement filter 40. To be more specific, for the firstthreshold of 35.6, the selection switch 30 switches the input port tothe output port connected to the picture quality improvement filter 40,if the estimated PSNR is less than the first threshold of 36.5 andswitches the input port to the output port connected to the externaloutput device, if the estimated PSNR is equal to or larger than thefirst threshold of 36.5.

When the MPEG-4/AVC decoder 10 is connected to the picture qualityimprovement filter 40, the picture quality improvement filter 40receives video data from the MPEG-4/AVC decoder 10, filters each pixelof the video frame, and calculates the difference between the filteredvalue and the original signal value of the pixel. Then if the differenceis less than the second predetermined threshold, the picture qualityimprovement filter 40 determines that the pixel is noise and cancels thenoise. If the difference is larger than the second threshold, thepicture quality improvement filter 40 determines that the pixel is anedge, not noise, and recovers the original decoded value by adding thedifference to the filtered value. Further, Further, the picture qualityimprovement filter 40 compensates for a filtering-caused decrease in thevalue of the edge.

In accordance with the exemplary embodiment of the present invention,the picture quality improvement filter 40 determines the picture qualityof the received video data by estimating the SNR of the video data, towhich the present invention is not limited. The picture quality levelcan be one of stepwise values matching to predetermined SNR ranges. Forexample, picture quality levels 1, 2, 3, 4, 5 and 6 can be setrespectively for an SNR range from 0 to below 10, an SNR range from 10to below 20, an SNR range from 20 to below 30, an SNR range from 30 tobelow 40, an SNR range from 40 to below 50, and an SNR range from 50 tobelow 60. In addition, the first threshold of the selection switch 30 isan SNR value that can be one of the SNR ranges.

FIG. 4 is a flowchart illustrating a video decoding method according toan exemplary embodiment of the present invention. It is assumed thatvideo data encoded by an MPEG-4/AVC encoder is received through acommunication device.

Referring to FIG. 4, upon receipt of the encoded data in step 10, thevideo decoder recovers color difference signal values of pixels includedin each video frame in an MPEG-4/AVC decoding scheme in step 11.

In step 13, the video decoder extracts information about the bit streamsize, type, and fragmentation state of each macro block from the videodata during the decoding and acquires picture quality estimationinformation based on the information. The picture quality estimationinformation includes information about the size of the video frame, thenumber of skip-mode macro blocks included in the video frame, and thenumber of fragmented macro blocks included in the video frame.

The video decoder estimates the SNR of the video frame based on thecorrelation between picture quality estimation information and SNR instep 15. For example, the PSNR of the video frame is estimated by

Cost(SIZE,SKIP,4 MV)=ƒ(SIZE)·α+ƒ(SKIP)·β+ƒ(4 MV)·γ  (2)

-   -   where α, β and γ are weights;    -   ƒ(x) is a standardization function defined as

${f(x)} = \frac{X - \mu}{\mu}$

-   -   -   where X is a target value and μ is an accumulated average.

That is, X is the bit stream byte size of the video frame (SIZE), thenumber of the skip-mode macro blocks in the video frame (SKIP), or thenumber of the 4-fragment macro blocks (4 MV), and μ is the accumulatedaverage of X. For instance, if 4 MV=10, 30 and 40 respectively in first,second and third video frames, X=40 for 4 MV and μ is the accumulatedaverage of the first and second video frames, i.e. 20 in the third videoframe.

In step 17, the video decoder compares the estimated PSNR with the firstpredetermined threshold (e.g. 36.5). If the estimated PSNR is less thanthe first threshold of 36.5, the video decoder performs step 19. If theestimated PSNR is equal to or larger than the first threshold of 36.5,the video decoder jumps to step 25.

In step 19, the picture quality improvement filter 40 of the videodecoder filters each pixel of the video frame and compares thedifference between the filtered value and the original value of thepixel with the second predetermined threshold, for noise cancellation.If the difference is less than the second threshold, the picture qualityimprovement filter 40 performs step 23. In the step 23, the picturequality improvement filter 40 determines that the pixel is noise andcancels the noise. If the difference is larger than the secondthreshold, the picture quality improvement filter 40 performs step 21.In the step 21, the picture quality improvement filter 40 determinesthat the pixel is an edge, not noise, and outputs the original decodedvalue by adding the difference to the filtered value.

In step 25, the video decoder outputs the video data decoded in step 11or the video data compensated in step 23 to an external output devicesuch as a display.

While in accordance with the exemplary embodiment of the presentinvention, the picture quality of the received video data is determinedby estimating the PSNR or other measure of quality, of the video data.The picture quality level can be determined as one of stepwise valuesmatching to predetermined SNR ranges. For example, picture qualitylevels 1, 2, 3, 4, 5 and 6 can be set respectively for an SNR range from0 to below 10, an SNR range from 10 to below 20, an SNR range from 20 tobelow 30, an SNR range from 30 to below 40, an SNR range from 40 tobelow 50, and an SNR range from 50 to below 60. In addition, thethreshold of step 17 is an SNR value, which can be one of the SNRranges.

While video data is encoded and decoded based on an MPEG-4/AVC standardin the exemplary embodiments of the present invention, to which thepresent invention is not limited, it is to be clearly understood thatthe present invention is also applicable to various videoencoding/decoding schemes such as H.263 and H.264.

Also, while the picture quality level of video data is determined byequation (2) in step 15, to which the present invention is not limited,the determination can be made in many ways based on the correlationbetween SNR and picture quality information extracted during decodingthe video data. For example, the SNRs and picture quality estimationinformation of a plurality of videos are measured, the consistency andregularity of the SNRs and the picture quality estimation informationare analyzed, and the correlation between SNR and picture qualityinformation is placed accordingly. How the correlation between SNR andpicture quality estimation information is set will be described, usingexperiment examples.

The video encoding and decoding experiments of the present invention arecarried out for typical seven videos (Container, Crew, Foremen, Harbor,Mobile, Soccer, and Stefan) under the conditions of image sizes, framerates, total frame numbers, data rates, and I-frame intervals set asillustrated in FIG. 5.

Referring to FIG. 5, an image size of QVGA (320×240 p) is set forExperiment 1, Experiment 2 and Experiment 3 and an image size of CIF(352×288 p) is set for Experiment 4 to Experiment 7. The frame rates,total frame numbers, data rates, and I-frame intervals of Experiment 1to Experiment 7 are the same, 30 fps, 300 frames, 384 kbps, and 30frames.

The videos are encoded in MPEG-4. Then the PSNRs of each video aremeasured and the average AVG and standard deviation STDDEV of the PSNRsare listed in FIG. 6. Also, for 300 video frames in each video type, thebyte sizes of bit streams SIZE, the numbers of skip-mode macro blocksSKIP, the numbers of intra-mode macro blocks INTRA, average motionvector powers MV_PWR, and the numbers of 4-fragment macro blocks 4 MVare measured and their averages are listed in FIG. 6.

Correlation coefficients between PSNR and SIZE, SKIP, INTRA, MV_PWR, and4 MV illustrated in FIG. 6 are computed by equation (3) and listed inFIG. 7.

${{Correlation}\left( {X,Y} \right)} = \frac{\sum{\left( {x - \overset{\_}{x}} \right)\left( {y - \overset{\_}{y}} \right)}}{\sqrt{\sum{\left( {x - \overset{\_}{x}} \right)^{2}\left( {y - \overset{\_}{y}} \right)^{2}}}}$X = AVG(array 1):PSNRy = AVG(array 2):SIZE, SKIP, INTRA, MV_PWR, 4 MV

As noted from Figure xxz PSNR increases with SIZE and with 4 MV whereasPSNR decreases with SKIP. Based on these experiment results, thecorrelation between PSNR and picture quality estimation information canbe set as equation (4), which can be standardized in different ways;

$\begin{matrix}{\frac{1}{PSNR} \propto {\left( \frac{1}{SIZE} \right) \cdot ({SKIP}) \cdot \left( \frac{1}{4\; {MV}} \right)}} & (4)\end{matrix}$

The above-described methods according to the present invention can berealized in hardware or as software or computer code that can be storedin a recording medium such as a CD ROM, an RAM, a floppy disk, a harddisk, or a magneto-optical disk or downloaded over a network, so thatthe methods described herein can be rendered in such software using ageneral purpose computer, or a special processor or in programmable ordedicated hardware, such as an ASIC or FPGA. As would be understood inthe art, the computer, the processor or the programmable hardwareinclude memory components, e.g., RAM, ROM, Flash, etc. that may store orreceive software or computer code that when accessed and executed by thecomputer, processor or hardware implement the processing methodsdescribed herein.

As is apparent from the above description, the present inventionadvantageously estimate the picture quality of video data based oninformation acquired during decoding encoded video data withoutadditional information representing the picture quality level (e.g. aPSNR). Further, compensation of the video data according to theestimated picture quality results in a high-quality video.

While the invention has been shown and described with reference tocertain exemplary embodiments of the present invention thereof, it willbe understood by those skilled in the art that various changes in formand details may be made therein without departing from the spirit andscope of the present invention as defined by the appended claims andtheir equivalents.

1. A method for decoding video data that is encoded by bit rate control,comprising: decoding the encoded video data; estimating picture qualityestimation information including information about a bit stream size ofa decoded video frame, the number of fragmented macro blocks included inthe video frame, and the number of skip-mode macro blocks included inthe video frame; determining the picture quality of the video data basedon a correlation between picture quality estimation information andSignal-to-Noise Ratio (SNR); and outputting the video data by applying apicture quality improving algorithm to the video data, if the determinedpicture quality is lower than a predetermined level.
 2. The method ofclaim 1, wherein the SNR is Peak Signal-to-Noise Ratio (PSNR).
 3. Themethod of claim 1, wherein the SNR is estimated by using a bit streambyte size of the video frame (SIZE), the number of the skip-mode macroblocks in the video frame (SKIP), and the number of the 4-fragment macroblocks (4 MV), and a picture quality of the video data is determinedbased on the estimated SNR.
 4. The method of claim 1, wherein thepicture quality determination comprises calculating an SNR decrease. 5.The method of claim 1, wherein the picture quality improving algorithmis a PSNR improving algorithm.
 6. The method of claim 1, wherein saidpicture quality improvement algorithm: determines a difference between afiltered value and a original signal value; determines whether saiddifference is less than a predetermined threshold; and cancels saidoriginal signal value as noise if said difference is less than saidpredetermined threshold.
 7. An apparatus for decoding video data that isencoded by bit rate control, comprising: a decoder for decoding theencoded video data; a picture quality detector for estimating picturequality estimation information including information about a bit streamsize of a decoded video frame, the number of fragmented macro blocksincluded in the video frame, and the number of skip-mode macro blocksincluded in the video frame, and measuring the picture quality of thevideo data based on a correlation between picture quality estimationinformation and Signal-to-Noise Ratio (SNR); a picture qualityimprovement filter for improving the picture quality of the video datareceived from the decoder; and a selection switch for switching thevideo data selectively to one of the picture quality improvement filterand an external device according to the picture quality of the videodata, wherein said video data is provided to the external device whenthe estimated picture quality is equal to or larger than a threshold. 8.The apparatus of claim 7, wherein the SNR is Peak Signal-to-Noise Ratio(PSNR).
 9. An apparatus of claim 7, wherein the picture quality detectorestimates an SNR by using a bit stream byte size of the video frame(SIZE), the number of the skip-mode macro blocks in the video frame(SKIP), and the number of the 4-fragment macro blocks (4 MV) anddetermines a picture quality of the video data based on the estimatedSNR.
 10. The apparatus of claim 7, wherein the picture quality detectormeasures the picture quality of the video data by calculating a decreasein an SNR estimated using the picture quality estimation information.11. The apparatus of claim 10, wherein the picture quality improvementfilter is a noise reduction filter.
 12. The apparatus of claim 7,wherein the picture quality improvement filter executes the steps of:determining a difference between a filtered value and a original signalvalue; determining whether said difference is is less than apredetermined threshold; canceling said original signal value as noiseif said difference is less than said predetermined threshold.
 13. Adevice for decoding video data that is encoded by bit rate control,comprising: a processor in communication with a memory, the memoryincluding code which when accessed by the process causes the process to:decode the encoded video data; evaluate picture quality estimationinformation including information about a bit stream size of a decodedvideo frame, the number of fragmented macro blocks included in the videoframe, and the number of skip-mode macro blocks included in the videoframe; determine the picture quality of the video data based on acorrelation between picture quality estimation information and aSignal-to-Noise Ratio (SNR); and output the video data by applying apicture quality improving algorithm to the video data, if the determinedpicture quality is lower than a predetermined level.
 14. The apparatusof claim 13, wherein the SNR is Peak Signal-to-Noise Ratio (PSNR). 15.The apparatus of claim 13, wherein the correlation between picturequality estimation information and SNR is given by using a bit streambyte size of the video frame (SIZE), the number of the skip-mode macroblocks in the video frame (SKIP), and the number of the 4-fragment macroblocks (4 MV).
 16. The apparatus of claim 13, wherein the picturequality determination comprises calculating an SNR decrease.
 17. Theapparatus of claim 13, wherein the picture quality improving algorithmis a PSNR improving algorithm.
 18. An apparatus for providing a decodedvideo output comprising: a processor in communication with a memory,said processor accessing code in said memory which provides instructionto said processor to execute the steps of: receiving and decoding anencoded video signal; determining a picture quality of said decodedvideo signal based on at least one of a bit stream size of a decodedvideo frame, the number of fragmented macro blocks included in the videoframe, and the number of skip-mode macro blocks included in the videoframe; correlating said picture quality with a Signal-to-Noise ratio;and outputting the decoded video data to a picture quality improvingalgorithm if the determined picture quality is greater than apredetermined level.
 19. The apparatus of claim 18, wherein saidimprovement algorithm further recovers the original decoded value byadding the difference to the filtered value.
 20. The apparatus of claim18, wherein said picture quality improvement algorithm: determines adifference between a filtered value and a original signal value;determines whether said difference is less than a predeterminedthreshold; and cancels said original signal value as noise if saiddifference is less than said predetermined threshold.